March 15th-made famous by William Shakespeare in his play, Julius Caesar. "Beware the Ides of March" words spoken to the emperor by a fortune teller as he headed for the Roman Capitol and ultimately his death at the hands of Brutus and a couple of others.
Since Shakespeare wrote those words the 15th March is thought of as a cursed day. In reality it was not originally so. "Kalends, Nones and Ides were ancient markers used to reference dates in relation to lunar phases. Ides simply referred to the first full moon of a given month, which usually fell between the 13th and 15th. In fact, the Ides of March once signified the new year, which meant celebrations and rejoicing."
Oddly Julius Caesar was the one who changed the traditional new year from March 15 to January, two years before he was killed.